1. Field of the Invention
This invention relates to an oscillator. Many communication devices including handy telephone and PHS etc. are used widely for general use. Frequency accuracy used in these devices is most important, and this invention provides a quartz oscillator a highly accurate frequency for use with these devices.
2. Description of Prior Art
A quartz oscillator is used as a frequency source up to now. But the prior art crystal quartz oscillator uses an inductive region of quartz vibrator. Therefore higher frequency more than the characteristics serial resonating frequency of the quartz oscillator is generated, and many sub-frequencies are accompanied for the reason of vibrating energies propagating outside of electrode thereon.
The is an obstacle for fabricating an accurate frequency oscillation source. On the other hand, an oscillator design for decreasing the loss term of quartz vibrator is adapted to make oscillation starting of oscillation easy. This amounts to making the electrode size great, and the sub-frequency generation is increased. So it is difficult to fabricate an accurate frequency oscillation source.
Most quartz oscillators use a thickness-shear mode vibration (in following, explained as AT mode vibration). But they have a characteristic accompanying the other vibrating mode. Especially, a flexure mode vibration accompanied causes a problem that the vibration frequency is much lower than the AT mode series vibration and temperature frequency change is great. Therefore it happens for the flexure mode vibration frequency to coincide with the AT mode series vibration in any temperature within a wide range temperature. Then energy transfer occurs between both modes of vibration. This is called mode coupling, and as the result the AT mode frequency is changed suddenly.
The sudden change of frequency in AT mode has been suppressed by avoiding the coupling between the AT mode and flexure mode. It is resolved by fabrication techniques as strict management of the outline size of the quartz blank (reference number 1 of FIG. 1, FIG. 2, FIG. 3) which affects most to the flexure mode series vibration or beveling cut of the cross-section of quartz vibrator (reference number of FIG. 2) for suppressing the flexure mode vibration. However they are not essential resolving methods, and in spite of the production, management many quartz blank having the coupling mode are frequently fabricated for the reason of dispersion of outline size and beveling form of crystal blank in the fabricating process. The quartz vibrator having the mode coupling is excepted at final measuring process thereof, therefore fabrication efficiency of prior art quartz vibrator is very bad. Higher accuracy of the frequency generation source is requested, the fabrication efficiency is greatly lowered. Therefore it is difficult to keep the product quantity, as the product quantity of accurate frequency source is unstable.